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IEEE1284_CONTROL(3)			    Functions			      IEEE1284_CONTROL(3)

       ieee1284_read_control, ieee1284_write_control, ieee1284_frob_control,
       ieee1284_do_nack_handshake - manipulate control lines

       #include <ieee1284.h>

       int ieee1284_read_control(struct parport *port);

       void ieee1284_write_control(struct parport *port, unsigned char ct);

       void ieee1284_frob_control(struct parport *port, unsigned char mask, unsigned char val);

       int ieee1284_do_nack_handshake(struct parport *port, unsigned char ct_before,
				      unsigned char ct_after, struct timeval *timeout);

       There are four control lines, three of which are usually inverted on PC-style ports. Where
       they differ, libieee1284 operates on the IEEE 1284 values, not the PC-style inverted
       values. The control lines are represented by the following enumeration:

	   enum ieee1284_control_bits
	     C1284_NSTROBE   = 0x01,
	     C1284_NAUTOFD   = 0x02,
	     C1284_NINIT     = 0x04,
	     C1284_NSELECTIN = 0x08,
	     /* To convert those values into PC-style register values, use this: */
	     C1284_INVERTED = (C1284_NSTROBE|

       These functions all act on the parallel port associated with port, which must be claimed.

       The current values on the control lines are available by calling ieee1284_read_control,
       and may be set by calling ieee1284_write_control.

       To adjust the values on a set of control lines, use ieee1284_frob_control. The effect of
       this can be expressed by: ctr = ((ctr & ~mask) ^ val); that is, the bits in mask are
       unset, and then those in val are inverted.

       The special function ieee1284_do_nack_handshake is for responding very quickly in a
       protocol where the peripheral sets nAck and the host must respond by setting a control
       line. Its operation, which relies on the host machine knowing which interrupt nAck
       generates, is as follows:

	1. Set the control lines as indicated in ct_before.

	2. Wait for nAck interrupt. If timeout elapses, return E1284_TIMEDOUT.

	3. Set the control lines as indicated in ct_after.

       On Linux using the ppdev driver, this is performed by the device driver in the kernel, and
       so is faster than normally possible in a user-space library.

       The return value of ieee1284_read_control, if non-negative, is a number representing the
       value on the control lines.

       Possible error codes for ieee1284_read_control:

	   The control lines of this port are not accessible by the application.

	   The port parameter is invalid (for instance, perhaps it is not claimed).

       Possible error codes for ieee1284_do_nack_handshake:

	   The handshake was successful.

	   This operation is not available on this port type or system. This could be because
	   port interrupts are not available, or because the underlying device driver does not
	   support the operation.

	   The port parameter is invalid (for instance, perhaps it is not claimed).

       Tim Waugh <twaugh@redhat.com>

       Copyright (C) 2001-2003 Tim Waugh

[FIXME: source] 			    06/17/2014			      IEEE1284_CONTROL(3)
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